This invention relates to snowmobile suspension systems, and more particularly to coupled suspension systems, and even more particularly to an apparatus, in the form of an after-market upgrade kit, that permits, when installed, quick and easily accessible coupling adjustment.
Tracked vehicles such as snowmobiles have rear suspension systems generally consisting of front and rear suspension arms pivotally mounted on shafts, which are rotatably connected to the frame of the snowmobile, and a slide frame, which comprises a pair of laterally spaced apart slide rails or longitudinal skids interconnected transversely on opposing lateral sides of the machine. The slide rails are in sliding contact with an endless belt which provides ice and snow surface contact and a friction drive for the snowmobile. In many current arrangements, front and rear suspension arms pivotally interconnect the chassis to the slide frame.
It is generally known in the art that independent movement of the front and rear suspension arms is less desirable than a suspension system in which the front and rear suspension arms are coupled. In an uncoupled suspension system, when the front suspension arm deflects as it contacts a bump, the independent rear suspension arm remains in its ride or fully extended position. This results in an angle of incidence between the slide rails and the bump. Unless the impact is so large that it compresses the rear suspension arm spring and shock absorber assembly, thereby flattening the angle of incidence, the slide rails will act as a ramp forcing the rear of the snowmobile upward. That is, with the slide rails angled in an upward incline due to the independent deflection of the front suspension arm, but not the rear suspension arm, the snowmobile will hop over the bump, imparting a secondary jolt which increases in intensity with the speed of the snowmobile. This secondary jolt also results in a loss of control and a reduction of the speed of the snowmobile.
On the other hand, a coupled suspension system is one in which, for example, the rear portion of the suspension system reacts (i.e., is coupled) to the compression experienced by the front portion of the suspension system as the snowmobile passes over a bump in the terrain. In effect, the bump is xe2x80x9ccommunicatedxe2x80x9d to the rear portion of the suspension, causing the rear portion to be pulled upward toward the chassis before the rear portion actually reaches the bump. This reduces the angle of incidence between the slide rail and the bump, which thereby reduces the secondary jolt experienced by the rider. As a result, a coupled suspension system provides for an improved ride because the coupled suspension is better suited to adjust to varying terrain conditions.
Manufacturers have developed a variety of ways to provide coupled suspension systems, which typically involve restricting the amount of longitudinal movement of the rear suspension arm. Such systems are shown in U.S. Pat. Nos. 5,881,834, 5,692,579, 5,667,031, and 5,944,134, which are incorporated herein by reference.
The suspension system disclosed in Polaris"" U.S. Pat. No. 5,692,579 (xe2x80x9c""579xe2x80x9d) patent is shown in FIGS. 1-4 where FIG. 1 shows the overall suspension system removed from the snowmobile, and FIGS. 2-4 show the design approach used to couple the suspension system. As disclosed in the ""579 patent and depicted in FIGS. 2 and 4, the linkage of the rear suspension arm 20 with the lower pivot arm 26 permits the front of the slide rails 10 to rise substantially independently of the rear portion of slide rails. During this independent movement of the front portion of the suspension, the lower pivot arm 26 pivots from the rearward position shown in solid lines in FIG. 2 to the forward position depicted in broken lines. At the point which the front surface 27 of the lower pivot arm 26 engages the front adjuster block 30, further independent upward movement of the front end of the suspension is prevented. That is, further upward movement of the front of the slide rails 10 is mechanically linked through the adjuster block 30 to the rear suspension arm 20, causing upward movement of the rear of the suspension (the rate of upward movement of the rear of the suspension may or may not be equal to the rate of movement of the front of the suspension, depending on the specific geometric configuration of the system).
The degree of independent movement afforded to the front of the suspension rails 10 is dependent on the distance between the rear stop 32 and the front adjuster block 30 in comparison to the width of the lower pivot arm 26. The rear surface 31 of the front adjuster block 30 thus provides a limit on the relative forward movement of the lower end of the suspension arm 20 with respect to the slide rail 10.
The Polaris(copyright) system of the ""579 patent further provides variability to the position of this limit, thereby giving the rider some control over the performance characteristics of the suspension. This variability is provided by using rectangular adjuster block 30, which has four surfaces that are each positioned at varying distances from the block""s central mounting point, as indicated by distances xe2x80x9cd1xe2x80x9d through xe2x80x9cd4xe2x80x9d in FIG. 4. By rotating the block to select one of the surfaces, the position of the limit with respect to the lower end of the suspension arm 20 can be controlled.
However, with the above Polaris(copyright) system, it is difficult for the rider to make a desired adjustment to the adjuster block 30, especially when the rider is in the field. To make an adjustment, the rider must first loosen the central mounting point (a bolt). Then, the rider must manage to rotate adjuster block 30, either with his fingers or with the aid of another tool, to the desired location, and then retighten the central mounting point. The rider must then repeat these steps for the adjuster block on the opposite side of the slide rail. Considering that the rider may wish to make such adjustments while in the field, where he/she would encounter other obstacles, such as deep snow, cold weather, and generally unfavorable conditions for handling tools and equipment, it is apparent that making such adjustments to the adjustable block 30 in order to compensate for differing terrain conditions is difficult with the above Polaris(copyright) system.
It is therefore the object of this invention to provide an apparatus, in the form of an after-market upgrade kit, for installation onto a coupled snowmobile suspension system of the kind described in U.S. Pat. No. 5,692,579 that, when installed, allows for a quick and easy adjustment of the front to rear coupling.
It is further an object of the present invention to provide an apparatus, in the form of an after-market upgrade kit, specifically configured to be installed onto the Polaris(copyright) line of snowmobiles.
It is the object of the present invention, therefore, to provide an apparatus and an after-market upgrade kit constructed and arranged to be installed onto a coupled snowmobile suspension. The upgrade kit includes a shaft having an axis of rotation, a pair of coupling blocks, and an indexer plate. The coupling blocks are adapted to be fixedly connected relative to the axis of rotation at each end of the shaft so that a torque in the shaft will be transmitted to the coupling blocks. The coupling blocks have a plurality of sides corresponding to a plurality of positions of the coupling blocks, each of the sides being located at a different distance from the axis of the shaft when the coupling blocks are connected to the shaft. The indexer plate is adapted to engage one of the coupling blocks at a selected positions of the coupling blocks. The shaft is constructed and arranged to be mounted between a longitudinal pair of slide rails of the snowmobile suspension, and the coupling blocks are adapted to be rotated about the axis to thereby adjust the coupling of the snowmobile.
Other objects and advantages of the present invention will be realized in accordance with the following detailed description, appended drawings, and claims.